The present invention relates to a method for producing a wheel rim of an automotive vehicle.
As a wheel rim of an automative vehicle, there is known, for example, the wheel rim having the configuration shown in FIG. 1. Referring to FIG. 1, flange portions F.sub.1 and F.sub.2 are formed on both sides of a cylindrical well portion W positioned around the center of the wheel rim H, and include first step portions a.sub.1 and a.sub.2, first side wall portions b.sub.1 and b.sub.2, second step portions c.sub.1 and c.sub.2, and second side wall portions d.sub.1 and d.sub.2 or rim end portions, respectively, formed into step shape having two steps in turn from both ends of the well portion W to opening ends of the wheel rim H. The first side wall portions b.sub.1 and b.sub.2 of the flange portions F.sub.1 and F.sub.2 include hump portions h.sub.1 and h.sub.2 curved and projected outward to secure a tire (not shown in the drawing) on the wheel rim H, and further, the second side wall portions d.sub.1 and d.sub.2 or the rim end portions are curved so as to project outward.
When this kind of wheel rim H is produced, a cylindrical body formed of a metal material such as an aluminium alloy and having the same diameter as the well portion W has previously been press worked separately at both ends several times to enlarge the diameter of the cylindrical body, thereby gradually forming both the end portions into the shape of the flange portions F.sub.1 and F.sub.2 described above. More particularly, in the above press working, a side die is fitted to an outer peripheral surface of the cylindrical body and a punch is inserted into the cylindrical body in its axial direction. Both the end portions of the cylindrical body are separately pressed toward the side die by the punch to form the end portions into a prescribed shape. These operations are repeated several times, whereby both the end portions of the cylindrical body are formed into the shape of the flange portions F.sub.1 and F.sub.2.
In the formation of the hump portions h.sub.1 and h.sub.2 and the rim end portions d.sub.1 and d.sub.2 of the wheel rim H, portions corresponding to the above hump portions h.sub.1 and h.sub.2 of the first side wall portions b.sub.1 and b.sub.2 are curved so as to project outward to form the hump portions h.sub.1 and h.sub.2, and the second side wall portions d.sub.1 and d.sub.2 of the flange portions F.sub.1 and F.sub.2 are curved so as to project outward to form the above rim end portions d.sub.1 and d.sub.2.
However, according to the press working method for forming the wheel rim H in which the punch is merely inserted into the cylindrical body and both the end portions of the cylindrical body are radially pressed thereby as described above, if it is tried to form both the end portions into a shape similar to that of the flange portions F.sub.1 and F.sub.2 at one time, there is a possibility of generation of harmful effects such as buckling due to the action of high tensile load on both the end portions of the cylindrical body. For this reason, it is necessary that both the end portions of the cylindrical body are separately press worked several times as described above. A large number of working steps are therefore required, which results in an obstacle to an improvement in manufacturing efficiency of the wheel rim H.
It is therefore an object of the present invention to provide a method by which such a disadvantage can be canceled and a wheel rim can be efficiently produced with less working steps than prior-art methods.